Question

java.lang.annotation.ElementType:

A program element type. The constants of this enumerated type provide a simple classification of the declared elements in a Java program. These constants are used with the Target meta-annotation type to specify where it is legal to use an annotation type.

There are the following constants:

• ANNOTATION_TYPE – Annotation type declaration
• CONSTRUCTOR – Constructor declaration
• FIELD – Field declaration (includes enum constants)
• LOCAL_VARIABLE – Local variable declaration
• METHOD – Method declaration
• PACKAGE – Package declaration
• PARAMETER – Parameter declaration
• TYPE – Class, interface (including annotation type), or enum declaration

Can someone explain what each of them are (where they’d be annotated in actual code)?

Answer 1

This summarizes the main ones:

@CustomTypeAnnotation
public class MyAnnotatedClass {
  @CustomFieldAnnotation
  private String foo;

  @CustomConstructorAnnotation
  public MyAnnotatedClass() {
  }

  @CustomMethodAnnotation
  public String bar(@CustomParameterAnnotation String str) {
    @CustomLocalVariableAnnotation String asdf = "asdf";
    return asdf + str;
  }
}

ANNOTATION_TYPE is an annotation on another annotation, like this:

@CustomAnnotationTypeAnnotation
public @interface SomeAnnotation {
  ..
}

Package is defined in a package-info.java file in the package, like this:

@CustomPackageLevelAnnotation
package com.some.package;

import com.some.package.annotation.PackageLevelAnnotation;

For more info on PACKAGE annotations see here and here.